No matter how many times he addresses it or gives major speeches about it, the 'pastor question' pursues him in the Jewish community -- and beyond.
And it's the one that still has many Jewish Democrats on the fence if they've not yet voted in a primary or if they are looking ahead to November if he clinches the Democratic nomination.
On April 16, Obama took a new stab at it, seeking to further distance himself from the Rev. Jeremiah Wright Jr., the clergyman the whole world now knows has spewed venom toward the United States and Israel.
He was 'my pastor,' not 'my spiritual adviser,' Obama told some 75 Jewish communal leaders gathered at this city's Rodeph Shalom synagogue in an apparent effort to downplay the role Wright played in his life.
Interestingly, he didn't go quite so far in the debate here later that night with U.S. Sen. Hillary Rodham Clinton (D-N.Y.), when asked once again to address the issue.
The Obama campaign knows the Wright question continues to rile, which is why, in part, the candidate and his emissaries have gone to such extraordinary lengths in reaching out to the Jewish community in Pennsylvania prior to its April 22 primary and beyond to emphasize his commitment to Israel and Jewish issues.
Obama has been gaining support in the Jewish community, with recent polls suggesting a near split among Jews between the Illinois senator and Clinton, who once enjoyed a strong lead in the community.
Clinton still got the support of the bulk of the Jewish establishment in Pennsylvania and leaders of the local federation were visibly absent from the special Obama event.
But Obama is also enormously popular among segments of the Jewish community. Jewish supporters say they are energized by his vision and inspired by the belief he will seek a new path in domestic politics and foreign policy.
Many of these supporters look past the Wright issue and ask, as Obama does, that he be judged on his own record and statements, which show a strong pro-Israel stance and a commitment to strong black-Jewish relations.
But the question of why he stayed at a church whose pastor honored Louis Farrakhan and published Hamas op-eds -- and why he continued to expose his family to those sentiments -- continues to gnaw, even among some of his supporters.
At the synagogue gathering, after reiterating his oft-stated positions on Israel, Iran and Iraq -- uncharacteristically reading from prepared remarks -- Obama spent considerable time trying to get beyond the pastor question.
Asserting that he was not aware of Wright's offensive comments until he began running for president, Obama said that upon learning of them, he 'shared with him my deep concerns' about those remarks.
At the same time, Obama also reiterated that the 'the caricature that has been presented' of Wright 'is not an accurate depiction of who is he as a pastor.'
Obama went further, however, dismissing the notion that he said is often put forward -- that Wright is his 'spiritual adviser.'
'He was my pastor, which meant that when I went to church,' he led the sermons, many of which, he added, were 'insightful' when they related to social justice and other such topics.
'The sermons that were a source of controversy were deeply disturbing to me' and 'I told him they were disturbing and wrong.'
So why didn't he leave?
Noting that Wright was just months away from retirement when he heard about them, Obama said he was faced with a decision about how to handle the situation. After denouncing his pastor's comments and quietly expressing concern, he said he chose to 'recognize that you are still part of a broader church community that was going to be transitioning.'
At another point during the morning, Obama asked his audience 'to not base decisions on who to support or not on e-mails or superficial characteristics or associations that are tangential to who I am or what I believe in.'
Many of the concerns raised about him, he said, have been generated by "scurrilous e-mails," and by the fact that his middle name is Hussein and that he is an African American in an era of strained relations between the black and Jewish communities on some issues.
'I just want to emphasize I guess what's in my heart, which is that my ties to the Jewish community are not political,' he said. 'There's a kinship and a sense of shared commitments that pre-dates my politics and will extend beyond this particular election.'
Throughout the session, Obama appeared tired, the pace of the campaign obviously taking a toll. There was generous applause throughout his talk and a standing ovation at the end. But as one might expect from a Jewish audience, the reaction was mixed.
For Nancy Gordon, an ardent Clinton supporter, Obama was not convincing. She said she "wasn't persuaded by his answer" to the question she asked about his pastor.
Gordon, the chair of the Philadelphia chapter of JACPAC, a political action committee that supports candidates based on their positions on Israel and reproductive rights, said she "didn't find it credible" that he didn't know about Wright's offensive remarks before he began his campaign.
By supporting Clinton, she said, "I'm going with more experience and more knowledge on all the issues I care about, including Israel."
Obama did more to move Max Schapiro, a University of Pennsylvania student who chairs his Hillel's Israel committee.
Before the talk, Schapiro said he was undecided on a candidate, but he was impressed by Obama's "charisma and sense of hope." Noting that Israel was his No. 1 issue, he was impressed as well by Obama's record on Israel, but needed to hear more.After the session, Schapiro said Obama was convincing in saying that voters should judge him based on his record and policies, not on "the background chatter."
The verdict is still out on how he'll pull the lever next week, he said, but "this was very helpful. I'm that much closer."
Rabbi Philip Warmflash also felt more at ease after hearing the candidate.
Prior to the senator's entrance, Warmflash noted his family has "a Hillary sign on our lawn and I'm here because I want to be convinced otherwise -- or at least to be more comfortable with voting for Obama in the general election" if he is nominated.
Afterward, Warmflash said he "felt much better about him."
"He showed an understanding of issues and didn't present them glibly," said Warmflash, the executive director of the Jewish Outreach Partnership.
Warmflash may not quite be ready to pull the Clinton sign from his lawn, but Wednesday's event is "making me think about it more."
"If I don't vote for him this time," he said, "I would feel OK -- even good -- about voting for him the next time."